1. Field of the Invention
The present invention relates to a semiconductor light-emitting device including a photodetecting device for detecting emission light, and more specifically, a semiconductor light-emitting device suitably used in an application demanding high photodetection accuracy.
2. Description of the Related Art
In a semiconductor light-emitting device for an optical fiber, an optical disk or the like in a related art, as a part of the purpose of keeping the light output level of a semiconductor light-emitting element assembled in the semiconductor light-emitting device at a constant level, emission light from the semiconductor light-emitting element is detected by a photodetecting system. The photodetecting system can be formed by including a reflection plate branching a part of the emission light and a semiconductor photodetector detecting the branched light. However, in this case, in addition to the issue of an increase in the number of components, another issue is that it is necessary to arrange the reflection plate and the semiconductor photodetector in the semiconductor light-emitting device with high accuracy. Therefore, as one solution to solve such an issue, the formation of the semiconductor light-emitting element and the semiconductor photodetector as one unit can be considered.
However, when they are formed as one unit, the semiconductor photodetector may detect not only induced emission light which is supposed to be detected but also spontaneous emission light. In such a case, the light output level of the semiconductor light-emitting element measured on the basis of light detected by the semiconductor photodetector includes an error by the spontaneous emission light. Therefore, this method is not suitable for an application which is necessary to control the light output level with high accuracy.
Therefore, there is proposed in Japanese Patent No. 2877785 a technique of arranging a control layer in a semiconductor photodetector so as to block a part of spontaneous emission light inputted from a semiconductor light-emitting element before detecting the spontaneous emission light by the semiconductor photodetector.